That has not that much to do with it.
The real issue is that adult game development is just a hobby for most devs. If something changes in their life, like in Grinvald's case, changing circumstances in his day job, then the game development suffers.
It's very simple. If a person is making $3000 / month in a day job, then he must be able to make $6000 / month with his adult game development, due to the added risks (e.g. getting kicked off from Patreon) compared to a normal job, as well as the lack of pension and other social securities which a normal job normally offers.
There are very, very few devs who make anything close to these figures.